Food storage can be improved by keeping food in a container under vacuum. Keeping the food in a container under vacuum helps to protect the food from certain microorganisms and pests, as well as mold and fungus growth. Furthermore, it helps prevent the food from oxidizing, thereby maintaining the moisture level and aroma of the food. However, with systems of this type it is often difficult to open the storage container because the vacuum inside the container draws on the container lid. In addition, it is often not possible for the user to recognize whether the desired vacuum is still present in the storage container. Furthermore, it can be difficult to maintain an adequate vacuum in the storage container, particularly over a prolonged period of time.
Food storage container lids with venting or aerating valves for pressure equalization during heating in a microwave oven are known. For example, EP 0 633 196 A2 describes a mechanism of this type. The venting or aerating valves can be used to prevent the build-up of overpressure in the interior of a food storage container when it is heated. Such a build-up of overpressure typically occurs when there are aqueous liquids in the interior of the container, and the liquids evaporate during heating, thereby building up an overpressure in the container interior. The result can be that sauces or other food within the container can spurt out suddenly when the container lid is opened. EP 0 633 196 A2 proposes a venting valve in the lid of the food storage container. The venting valve is to be opened before the container is placed in a microwave oven. The water vapor which develops during heating can then escape unhindered through the valve, without a corresponding build-up of vapor pressure in the interior of the sealed container. It is not intended to achieve thereby the improved storage of food under vacuum, or the indication of the pressure level in the food storage container.
In EP 0 820 939 A1, the object is to provide a food storage container with venting capability, so that food stored inside the container can be safely heated in a microwave oven with the container lid closed. Unlike EP 0 633 196 A2, a valve mechanism is described which can be opened by way of a joint like a rocker. Hence all that is required is to press in the rocker lever for the valve to open with ease. Here, too, there is no intention to use the valve mechanism to improve the storage of food under vacuum or to indicate the pressure level in the food storage container.
EP 0 644 128 A1 describes a food storage container having a container lid with a recess in which several vent openings are formed. The vent openings are closed by a seal when a vacuum exists in the holding space. The seal has pin-shaped anchor bars which project upwardly a small amount out of the recess and grow thicker at their ends. These anchor bars serve to lift the seal off the vent openings when air is to enter the holding space of the storage container from outside. Relatively high manual forces need to be applied to open this valve.
EP 0 644 128 A1 also describes a system for evacuating a container closable by a cover. EP 0 644 128 A1 describes a container with a cover that can be used to close the container and that includes a non-return valve located at the bottom of a depression. The annular periphery of the depression forms a sealing surface adapted to sealingly engage with a manually operable vacuum pump.
In accordance with FIG. 5 of EP 0 644 128 A1, if air is evacuated from the container space via the vacuum pump, then the non-return valve opens, and air flows from the container space through the valve into the vacuum pump. During the next idle stroke, after a non-return valve in the vacuum pump is closed, the air is transported outward to the atmosphere. The non-return valve in the cover closes as soon as the pressure in the container space is less than either the pressure in the vacuum pump or the atmospheric pressure. However, the non-return valve in the cover is also closed in the presence of atmospheric pressure in the container space as well as in the environment. The non-return valve opens as soon as the pressure in the vacuum pump is less than the pressure in the container space.
The non-return valve in the cover is formed by a diaphragm that is elastically pre-stressed in its initial position so that the diaphragm blocks the flow path when the diaphragm is in the rest state. If there is a sufficient vacuum in the container space, which is evidenced by the pump becoming increasingly difficult to operate, then an operator can separate the suction connection of the vacuum pump from the suction connection in the cover. This is possible because after every stroke of the vacuum pump, the non-return valve closes again so that no appreciable suction action results at the coupling connection.
In this manner, food that is located in the container space may be preserved longer than would be the case under atmospheric pressure. In the evacuated state, the cover can no longer be separated from the container because the force on the sealing surface between the cover and container is too great, due to the existing pressure difference. As a result, in order to subsequently open the container to remove the food, the vacuum in the container space must first be removed. This is achieved by manually pulling on a pin formed on the sealing sleeve until the sealing surface of the valve lifts away from the valve seat. Accompanied by hissing noises, atmospheric air is now able to flow into the container space until the pressure in the atmosphere and the pressure container space are equalized. After the pressure has been equalized, the cover can be easily removed from the container, and food can be removed from the container.
The arrangement described in EP 0 644 128 A1 can result in different vacuum pressures being produced in the container space via the manually operated vacuum pump, depending on the force exerted by an operator, and on the number of strokes that are completed at the vacuum pump. If in this process the vacuum becomes too strong in the container space, then bacteria that can attack the food can form in the container space. In fact, practice has shown that optimal storage life values may only be achieved within a certain pressure range in the container space. The arrangement described in EP 0 644 128 A1 can also result in other media (e.g. water) being transported by the vacuum pump, which can contaminate the food.
WO 88/00560 describes an opening mechanism for a plastic beverage can, and allows for a kind of visual check of pressure level. The beverage can has a plastic lid (the lids involved tend to be plastic, since one object is to avoid using metal lids) which bulges outward when the pressure inside the container is above atmospheric pressure. Such an arrangement does not allow for any quantitative conclusions about the magnitude of the pressure above atmospheric inside the container. Pressure equalization can occur by opening a venting valve, making it easier to subsequently remove the entire lid. The equalization of overpressure in the container interior (as a result of carbonated beverages, for example) plays a role in this case. This opening mechanism does not, however, allow for re-closure and the corresponding build-up of pressure.
CH 304 374 discloses a closure lid for an aluminum sterilizing container. The lid has an essentially circular-ring-shaped configuration, and is mounted on a cylindrical aluminum container. A rubber seal is placed between the edge of the lid and the upper brim of the container. In the middle of the container lid there is an additional opening which is covered by a rubber cap. The rubber cap provides a visual check, indicating whether there is a vacuum inside the container. As long as the pressure inside the container is adequately below atmospheric pressure, the rubber cap bulges inward a corresponding amount. This bulge diminishes continually as the vacuum decreases. Hence it is difficult for the observer to decide whether the pressure level inside the container is adequate for ensuring the freshness of the food inside the container.
DE 100 60 999 C1 describes a food storage container including a container lid with an opening mechanism for ventilating the evacuated container before it is opened. According to one embodiment, a sealing tongue is raised up from a vent via a driver. The sealing membrane and a pressure indicator are fastened directly on the container lid. The opening tab is connected non-releasably to the container lid via a film hinge. This mechanism provides an improved possibility for storing food under vacuum. The opening of the lid is facilitated by prior ventilation and the pressure indicator indicates the state of pressure in the container interior. However, disadvantages of this mechanism include the costly installation of the sealing components directly on the container lid, and the complicated driver mechanism of the one-way valve, which is susceptible to defects. Furthermore, the possibility of exchanging the valve mechanism is limited.
Finally, U.S. Pat. No. 5,195,427 describes another container evacuation system. U.S. Pat. No. 5,195,427 describes a vacuum container for storing food that is sealable in an airtight manner by a cover. A valve formed in a flow channel and functioning as a non-return valve is also located in the cover, as already described. The difference with respect to the previously described related art is essentially only that an electric vacuum pump held in the hand of an operator is used in the system, instead of a manually operated vacuum pump. To evacuate the container space, the pump is positioned or coupled in a sealing manner at the suction opening of the cover. The container evacuation system described in U.S. Pat. No. 5,195,427 can result in, as described above, an undesirably high vacuum being created in the container space. In some cases, an undesirably high vacuum can adversely affect the storage life of food in the container. The vacuum pump described in U.S. Pat. No. 5,195,427 can also transport liquid food, for example, when the suction connection is submerged in water, cream, etc., and is then activated.